1. Field
This application relates to sputtering systems, such as sputtering systems used to deposit thin films on substrates during the fabrication of integrated circuits, solar cells, flat panel displays, etc.
2. Related Arts
Sputtering systems are well known in the art. An example of a sputtering system having a linear scan magnetron is disclosed in U.S. Pat. No. 5,873,989, in which a magnetron sputtering source for depositing a material onto a substrate includes a target from which the material is sputtered, a magnet assembly disposed in proximity to the target for confining a plasma at the surface of the target and a drive assembly for scanning the magnet assembly relative to the target. The sputtering process relies on the creation of a gaseous plasma and then accelerating the ions from this plasma into the target. The source material of the target is eroded by the arriving ions via energy transfer and is ejected in the form of neutral particles—either individual atoms, clusters of atoms or molecules. As these neutral particles are ejected they will travel in a straight line to impact and coat the surface of the substrate as desired.
One of the problems to be resolved in such a system is the uniformity of the film that is formed on the substrate. Another problem to be resolved in such a system is target utilization. Specifically, since the magnets of linear magnetrons scans back and forth, excessive sputtering occurs at both edges of the target, generating two deep grooves along, i.e., parallel to, the scan direction. Consequently, the target has to be replaced, even though the majority of the surface of the target is still usable. Various methods for combating this phenomenon are disclosed in the above cited '989 patent.
However, another target utilization issue that has not been previously addressed is the erosion caused at the edges of the scan cycle. That is, when the magnets reach an end of the target, the scan direction is reversed. In order to achieve film uniformity, the '989 patent suggests to slow the scan speed towards either end of the target. However, this leads to increased sputtering of the target, leading to excessive erosion at both ends of the target in a direction perpendicular to the scan direction.
Accordingly, there is a need in the art for a sputtering system that enables uniform film deposition and increased target utilization.